Helen _____ her keys in the office so she had to wait until her husband _____ home.

[　　]

A．had left; comes

B．left; had come

C．had left; came

D．had left; would come

____ is known that thousands of Chinese worked in the gold mines the late 19th century.

[　　]

What ____ to you these days?

[　　]

A．have been happened

B．have happened

C．has happened

D．are happened

--What do you think made Mar upset?

--______ her new bicycle.

[　　]

I shall never forget those years _______ I lived in the country with the farmers, ______ has a great effect on my life.

[　　]

She heard a terrible noise, ____ brought her heart into her mouth.

[　　]

There was _______ to prevent the accident.

[　　]

A．something could do

B．anything we could do

C．nothing we couldn't do

D．nothing we could do

The book _____ is not in the library.

[　　]

It was during the Second World War ____ he died.

[　　]

____ he made up his mind that heavy objects fell faster than light ones, he taught it as a truth to his students.

[　　]